The genetic information content of mitochondrial DNAs (mtDNA) of some phylogenetically diverse animals and plants will be determined by renaturation kinetic studies. Restriction endonuclease methodology together with a variety of electron microscope techniques will be employed to study recombination and replication of mtDNA of Drosophila and rat. Various physiochemical techniques, including renaturation kinetic determinations, will be employed to try to establish whether all of the circular molecules of kinetoplast DNA of individual species of Trypanosoma and Crithidia carry the same genetic information. Hybridization studies will be made to determine whether and to what extent circular kinetoplast DNAs of Trypanosoma and Crithidia have nucleotide sequence homologies. Kinetoplast DNA of Crithidia consists of associations of approximately 27,000 topologically interlocked 0.8 micron circular molecules. Density labeling, autoradiography, melting profiles, and electron microscopy will be employed to try to determine whether DNA doubling involves replication of every circle or sequential replication of a few circles. Electron microscope autoradiography will be used to try to gain information concerning the pattern of kinetoplast DNA synthesis in situ. An attempt will be made to determine whether kinetoplast DNA of Crithidia is transcribed and if so whether the transcription product is ribosomal RNA, messenger RNA, or transfer RNA. BIBLIOGRAPHIC REFERENCES: Wolstenholme, D.R., H.C. Renger, J.E. Manning and D.L. Fouts. 1974. Kinetoplast DNA of Crithidia. J. Protozool. 21: 622-631. Fouts, D.L., J.E. Manning and D.R. Wolstenholme. 1975. Physicochemical properties of Kinetoplast DNA from Crithidia acanthocephali, Crithidia luciliae and Trypanosoma lewisi. J. Cell Biol. 67: in press.